Manufacture of pure urea



Patented Feb. 14, 1928. I

UNITED STATES PATENT OFFICE.

LEOPOIJD BUB, 0F MANNHEIM, GERMANY, ASSIGNOR TO I. G. FARBENINDUSTRIE AK- TIENGESELLSGHAFT, OF FRANKFORT-ON-THE-MAIN, GERMANY.

MANUFACTURE or'ronn UREA.

No Drawing. Application filed November 9, 1925,'Seria1 No. 68,022, and in Germany November 15, 1924.

color. In order to obtain a pure product, it

was hitherto necessary to dissolve theurea and to purify it by means of animal charcoal.

I *have now found that pure, white or colorless urea canbe obtained by treating concentrated solution-sot technical urea with I oxidizing agentsin the presence ofammonia. Generally, small quantities of ammonia are's'ufiicient, but at least about to 1 per cent-should be employed. .As oxidizing s.

'w icliitwould be difiicult to separate from such' as leave no" soluble residues the urea, are preferred, for example air, oxygen, m'anganese dioxid and the like which practically no urea is lost by sapoiiification.

By the methodexplained above, especially the compoundsof heavy metals are precipitated practically completely in a form in which they can easily be separated. Afterseparation from the .preci itate by filtration,

centrifuging or any suita le means, a 'cIear, colorless solution s obtainedfrom which by crystallizationor complete evaporation, a

pure, snow-white urea is obtained.

The following'example serves to further ill'ustratetlie nature ofg-my invention which however is not restricted .to'this example.

5000 litres of a urea solution, as itis obtained in the manufacturing process, containing .7 0 per cent, by weight, ofurea'and about 1.5 per cent of ammonia, are oxidized with air at the rate of 120 cubic metres per hour at a temperature of about 70 degrees to 7 5 degrees centigrade; The air is tangentially intro need through several fine nozzles into the solution which is vigorously stirred up thereby. The oxidation is complete after 1 to 2 hours and the solution is then filtered wh le still hot.. By evaporation or'crystallization a pure, white urea is obtained.

I claim: I I 1. The process of manufacturing colorless urea which consists in treating a con'centrated solution of impure urea with oxidiz ing agents in the presence of ammonia and separating the urea. solution from the .pre-

cipitated impurities the oxidizing agent and temperature being so chosen that practically ,no conversion of urea takes place.

2. The process of manufacturing colorless urea which COIlSlStSilIl treating a concentrated solution of impure urea with an oxidizing age'nt leaving no soluble products l e-- hindjand not chemically influencing the urea, in the presence of ammonia and at a moder ately elevated. temperature but lower than thatat WhlCh any substantial saponification of the urea would occur, and separating the urea solution from the ties. V

3. The process of manufacturing colourless urea which consists in treating a concen trated solution of impure ureawith a gaseprecipitated impurious oxidizing agent in the presence of am-. monia and separating the urea solution from the precipitated impurities, the oxidizing agent and temperature being so chosen, that practically no conversion of urea takes place.

4. The process of manufacturing colourless ureawhich consists in treating a concentratedsolution of impure urea with a gaseous oxidizing agent not chemically influencing the urea, in the presenceof-ammonia and 1 my hand.

LEoPoLD BUB. 

